1. Field of the Invention
The present invention relates to the connection of concrete foundations and tubular poles and their installation.
2. Description of Prior Art
Tubular poles have been used in many applications such as electrical transmission and distribution lines, electrical substation structure supports, outdoor lighting poles, and billboard supports. The tubular poles were normally made of steel, but any other suitable material could be used such as aluminum or fiberglass. The poles were normally six, eight or twelve sided and tapered Round tapered poles were common for smaller diameter poles. In some cases non-tapered poles have been used. The poles have been normally supported by drilled shaft foundations (caissons). There have been, so far as is known, three methods to anchor the poles: anchor bolts, direct embedment and direct burial. With anchor bolt foundations, a reinforcing bar cage was installed, and encased within a drilled bore hole which was then filled with concrete. A group of long steel bolts joined by a setting template were stabbed into the fresh concrete before the concrete had set. Once the concrete had set the bolts projected out of the concrete and fitted through a steel baseplate welded or bolted to the bottom of the pole. The number of bolts varied with the size of bolt used and the structural loads on the pole. The anchor bolts were fastened to the baseplate with one or two nuts.
The direct embedded method connected the pole to a drilled shaft foundation by embedding the bottom end of the pole in the concrete foundation. A direct embedded pole was connected to foundation by extending the pole into the foundation normally below ground. The construction of a direct embedded pole required supporting the pole at its desired position in the concrete until the concrete set up.
A direct buried pole did not have a concrete foundation. It was buried along its base portion in a hole augured in the earth. The backfill material used to bury the pole base could be either natural earth or a specially selected backfill material, such as sand, gravel, cement, stabilized sand or concrete. The inability to compact the backfill material at great depths limited its use to lower structural loads than other methods.
Where more than one line circuit was to be supported by a pole, the foundation was required to be of considerably larger diameter than the pole, increasing material costs considerably. Another problem present with anchor bolt foundations and their size was the difficulty of finding a suitable location for them. Personnel were concerned with finding a site for a ten foot or so diameter foundation pole into a right of way already full of buried wires and pipes, as well as ditches, roads, sidewalks and other surface obstructions.